JPH0380871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention allows a predetermined gas to be adsorbed onto the surface of a substrate,
The present invention relates to a novel photochemical thin film production method that allows fine control of the deposited layer by depositing the film using the adsorbed molecules.

The method of activating a gas through a photochemical reaction and depositing the target substance on the substrate surface to form a thin film is superior to conventional methods because it can be processed at low temperatures, there is no damage due to the impact of charged particles, and it has photochemical selectivity. In recent years, rapid progress has been made in recent years due to the fact that it has become possible to perform non-invasive treatments, and it is easy to select the reaction process and control film formation.

Conventional photochemical thin film manufacturing methods can be roughly divided into two methods. That is, there are two methods: a substrate heating method in which deposition is achieved by heating a substrate with radiation and thermally decomposing a predetermined gas, and a photodecomposition method in which deposition is achieved by photolyzing a predetermined gas.

In the substrate heating method, the principle is to heat the substrate with radiation. This is contrary to the most important advantage of photochemical reactions, which is the low temperature of the treatment process, and therefore the benefits of using this method cannot be expected to be significant.

On the other hand, the photodecomposition method utilizes the fact that a decomposition reaction occurs in a space filled with a predetermined gas through which radiation passes, and decomposition products are deposited on the substrate surface. Therefore, while the essence of film growth should originally proceed as a surface reaction, the reaction by photolysis is a spatially resolved reaction, and for this reason it is essentially extremely difficult to control film formation with this method. be.

In both the substrate heating method and the photolysis method, it goes without saying that the epitaxial growth of the film, as well as the film thickness,
Control of membrane quality is difficult in both cases, and it is impossible to obtain membranes with high added value using these methods.

Currently, it is common knowledge that creating high-quality epitaxial films requires extremely expensive equipment and extremely advanced technology, and the initial cost and running cost of the equipment are extremely high. . And countermeasures have become urgent.

The present invention is characterized by increasing and facilitating the controllability of film formation by decomposing a predetermined substance adsorbed on the substrate surface by a photochemical reaction on the substrate surface and forming a film.The purpose of this invention is to improve film thickness and film quality. Another object of the present invention is to facilitate the production of high-quality epitaxial films, superlattice films, etc.

The present invention was made based on the new knowledge discovered by the inventor of the present application, that when molecules adsorbed on the surface of a substrate are decomposed by radiation, they form a film on the spot. "Cleaning the substrate surface by degassing", "Adsorption of desired gas to the clean substrate surface", "Controlling the amount of adsorption", "Elimination of unnecessary molecules from the vicinity of the substrate surface", "Irradiation of radiation This process involves the creation of layered films, multilayer films, crystal growth films, superlattice films, etc. whose film thickness is controlled down to the atomic level, through the process of "making adsorbed molecules into a film" or through the accumulation of such processes. be. The details of the method will be explained below using Examples.

FIG. 1 is a membrane diagram showing one embodiment of the present invention. In the figure, 1 is an evacuation system for excluding the reaction chamber 2, and the evacuation system 1 is often one that can evacuate to an ultra-high vacuum (for example, a cryopump, an ion pump, etc., a turbo molecular pump, an oil pump, etc.). Rotary pumps are used redundantly, and the volume of the reaction chamber is determined by the pumping capacity of these devices and the required processing speed. (used for quality). The higher the pumping speed, the better.A lot of gas is adsorbed on the initial substrate surface, but after introducing the substrate 3 into the reaction chamber 2,
Initial degassing of the substrate surface is performed by heating the substrate holder at a pressure of 10 ^-5 Torr or less, with the addition of a temperature control mechanism if necessary (see Sections 1, 2, 3, and 4 of this application). A process of the invention).

Although it is impossible to create a surface completely free of adsorbed molecules, it is possible to create a so-called "clean surface" that poses no practical problems.
can be obtained by heating the substrate in a high vacuum and performing "temperature-programmed desorption" of the adsorbed molecules, and there is an extremely large amount of literature on this (for example, "Physics of Ultra-High Vacuum", translated by Goro Tominaga, Iwanami Shoten), It is a commonly used technique.

After sufficiently degassing the surface of the substrate 3, when a predetermined gas is introduced into the reaction chamber 2 from the gas introduction system 5, the gas can be adsorbed onto the substrate surface (see the first and second aspects of the present application). b process of invention).
At this time, the amount of adsorption can be controlled by controlling the temperature of the substrate and the pressure of the predetermined gas (step c of the first, second, third, and fourth inventions of the present application).

As is well known, the adsorption amount V of gas on the surface of a substance is generally defined by the temperature T and the gas pressure P, and it is known that the adsorption amount V can be controlled by setting T and P. (For example, DOHAYWARD
“CHEMISORPTION” (Btterworth & Co. Ltd.)
p160, p13) Next, the remaining gas excluding the adsorbed molecules is removed by the exhaust system 1, and the remaining gas other than the adsorbed molecules can be evacuated by a vacuum pump (step d of the first and second inventions of the present application). ). For a discussion on the potential energy of adsorption/desorption processes, see DOHAYWARD “CHEMISORPTION” above.
(Butterworth & Co. Ltd.) Familiar with p88. ) The pressure inside the reaction chamber is reduced to 10 ^-3 Torr or less again.

Now, the rate at which gas is adsorbed is high, while the rate at which the adsorbed gas is released is extremely slow. The method of the present invention takes advantage of this near-obvious phenomenon.

In this state, when appropriate radiation is irradiated from the light source 6 onto the substrate through the optical window 7 while controlling the temperature of the substrate 3 when necessary, the predetermined gas adsorbed on the substrate is decomposed. This is turned into a film (step e of the first, second, third, and fourth inventions of the present application).

This decomposition of gas and formation of a film on the substrate surface is a new phenomenon discovered by the inventor of the present application.

The process in which "adsorbed molecules or material surfaces" absorb radiation and decompose the adsorbed molecules is widely known in the field of photocatalysis (for example, Chemical Society of Japan, Chemistry Review, No. 39 "Inorganic Photochemistry"). . However, no literature has been found regarding the process by which it becomes a film after decomposition. (However, if this is a case of "free gas molecules," the process in which gases absorb synchrotron radiation and decompose to deposit a thin film on the substrate surface is well known, and it is already possible to
Used in CVD equipment. ) The quality of the film produced by film formation depends on the type of gas introduced and its component ratio, and the thickness of the film produced by film formation depends on the amount of previously adsorbed gas.

When a predetermined gas is adsorbed onto a clean surface, the surface is no longer a clean surface and the surface condition becomes different. Therefore, after a monomolecular layer is adsorbed, no adsorption occurs or only weak adsorption occurs. Therefore, the adsorption layer can be controlled by a monomolecular layer. (Langmuir's monomolecular adsorption theory. In fact, this theory agrees well with carbon monoxide, argon, and nitrogen on the silver surface.) Therefore, the film thickness produced by film formation can be controlled at the atomic level.

Therefore, when the conditions of gas introduction, exhaust, and radiation irradiation are set appropriately and the above steps are repeated an appropriate number of times, the thickness of each layer can be controlled at the atomic level.

According to experiments, by employing disilane gas as the predetermined gas, arranging a low-pressure mercury lamp (185 nm) as the light source 6, and using synthetic quartz glass as the optical window 7, this method has shown that a-
It was possible to create a Si:H film, and the film thickness could be easily controlled.

Latest literature (Jpn.J.Appl.Phys.22 (August) L544
(1983)), a-Si _0.2 C _0.8 :H/a-Si:H/
a-Si _0.2 C _0.8 : Thin a- in the heterostructure of H
It has been shown that the bandgap of Si:H layers (approximately 10 Å, 25 Å, and 50 Å) changes due to quantum size effects. This suggests that amorphous superlattice structures may become useful in the future. The above paper states that this thin heterostructure was created using a plasma CVD device, but it is difficult to stably obtain the desired film thickness with this plasma CVD method, and the theoretical thickness of 10, 25, and 50 Å is The film thickness of 10 Å, which is expected to be the most useful, has not been achieved.

Now, considering that the lattice constant of silicon is 5.4 Å, it becomes about 10 Å for two atomic layers and about 25 Å for 4 to 5 atomic layers.

As mentioned above, the a-Si:H multilayer film created in the example of the present invention can easily control the film thickness.
Since it can be performed for each atomic layer, it is possible to easily realize a multilayer film with a heterostructure as shown in the above-mentioned document, and its effects are expected.

Now, the following points should be noted in the present invention. That is, 8 in the figure is an infrared radiation plate, and this device is used to heat the substrate surface and/or to heat the molecules adsorbed on the optical window 7 (see Section 8 of this application).
2, h process of the invention of 4). However, in order to degas the optical window 7, in addition to the infrared radiation plate 8, conductive heating by the optical window heating heater 9 can also be used. Further effects can be achieved by using both types of heating together. Degassing of the optical window 7 is important in the present invention in order to prevent fogging of the optical window due to film deposition on the optical window, and degassing of the optical window is a major feature of the present invention.

Regarding synchrotron radiation, infrared synchrotron radiation is not unused in conventional methods. However, it is used as an optical device for heating the substrate, and is not intended to heat the optical window.The light used is infrared light from a CO ₂ laser, and the opposite optical window is exposed to this infrared light. In order to improve the transmission of light, materials such as NaCl that do not easily absorb infrared light are selected as window materials. (References Appl. Phys. Lett., 32,
254 (1978)) In contrast, in the present invention, an infrared heater "Sunny Beam" manufactured by Ebara Jitsugyo Co., Ltd., for example, is used as the infrared radiation plate, and a synthetic quartz glass "10 mm thick" manufactured by Toshiba Ceramics Corporation is used as the optical window. T-4040" is used. In other words, as shown in Figure 2, the emission spectrum A and absorption spectrum B of both of them have an overlapping part, so that the infrared radiation from the infrared radiation plate is sufficiently absorbed by the optical window, and the optical window is heated. Consideration will be given to ensuring that it is used.

The present invention has significant features not found in the prior art in the combination of the infrared light source and the optical window material and/or the conductive heating of the optical window.

As is clear from the above, in the present invention, conventional optical thin film manufacturing methods can be used as long as the intermediate step of evacuation is omitted. Therefore, when forming a film, it is possible to combine both the old and new methods, in which the parts with less added value are processed using the conventional method, and the parts with more important added value are processed with the present method. Furthermore, during the repetition of gas introduction, exhaust, and radiation irradiation, it is also possible to change the components of a predetermined gas midway through, thereby making it possible to create a so-called superlattice.

Further, in the present invention, when introducing a predetermined gas, the gas is introduced in the form of repeated pulses at appropriate intervals while the exhaust system is operating (step g of the third and fourth inventions of the present application), and the radiation is emitted. Alternately repeat gas introduction, evacuation, and irradiation by irradiating the substrate with continuous irradiation and/or in the form of repeating appropriately spaced pulses (e.g., excimer laser radiation is itself pulsed). A film of good quality can be obtained with the same effect as obtained in the above-mentioned process. Film formation in this case becomes even faster.

FIG. 3 is a schematic diagram of a photochemical thin film manufacturing apparatus used in experiments of the present invention. The reference numerals of each member are the same as in FIG.

As the evacuation system 1, a tarpo molecular pump 11 which is normally used for evacuation, an oil rotary pump for auxiliary evacuation, and an ion pump for high vacuum evacuation were used.

The turbo molecular pump 11 has about 400~500/
SGP (Screw Grooved Pump) with a displacement of sec and sufficiently effective exhaust characteristics even in the viscous flow region.
Using a built-in pump manufactured by Nichiden Anelva Co., Ltd., which is generally known as a Hi-Q turbo molecular pump,
The oil rotary pump 12 is T2063 manufactured by Alcatel.
Type (pumping speed approx. 1200/min), ion pump 1
For No. 3, a device manufactured by Nichiden Anelva Co., Ltd. with a pumping speed of approximately 500 was used.

A heater 22 and a thermocouple 2 are placed inside the substrate holder 4.
1 is built in, and the temperature of the substrate 3 is maintained at a predetermined level by controlling the current flowing through the heater 22 by PID control or PI control using a thyristor unit (not shown). Although not shown, a cooling mechanism is also built in in case it is desired to cool the substrate.

For reaction chamber 2, diameter D = 20 cm, flow length L = 45
A cylindrical one with a diameter of cm is used.

The present invention greatly contributes to the manufacture of semiconductor devices, and can be said to be an industrially useful invention.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for implementing the present invention. FIG. 2 shows the emission spectrum and absorption spectrum in that case. FIG. 3 shows a schematic diagram of the apparatus in which the present invention was tested. 1...Exhaust system, 6...Light source, 2...Reaction chamber, 7
...Optical window, 3...Substrate, 8...Infrared radiation plate,
4... Substrate holder, 9... Optical window heating heater, 5... Gas introduction system.

Claims (1)

4. A method for producing a photochemical thin film, characterized in that the discharge of gas in item d of claim 1 reduces the pressure inside the vacuum container to 10-3 Torr or less. 5. A method for producing a photochemical thin film, characterized in that the radiation irradiation in item e of claim 1 is performed intermittently at predetermined intervals. 6. A method of adsorbing a gas onto a substrate surface in a reaction chamber, activating the adsorbed molecules and/or the substrate surface with radiation and/or heat, and depositing a target substance on the substrate surface, comprising: A method for producing a photochemical thin film, comprising steps b, c, d, e, and h. a. A step in which the reaction chamber is evacuated to degas molecules adsorbed on the substrate surface. b. A process of filling the reaction chamber with the gas in order to adsorb the gas after degassing the surface of the substrate; c) A process of maintaining the substrate at a predetermined temperature in order to control the amount of adsorption of the gas. d. A process of exhausting the gas remaining in the reaction chamber after the gas is adsorbed onto the surface of the substrate. e. A process of irradiating the temperature-controlled substrate with radiation of a selected wavelength and/or wavelength band emitted from a light source such as a lamp, laser, and/or infrared radiation plate to deposit a target substance on the surface of the substrate. h Exhaust the gas to below 10-3Torr,
A process of heating an optical window through which radiation passes by irradiating radiation and/or using a heat conduction method under the following pressure to degas the gas adsorbed on the side wall surface of the reaction chamber of the optical window. 7. A method in which a gas is adsorbed onto a substrate surface in a reaction chamber, the adsorbed molecules and/or the substrate surface are activated by radiation and/or heat, and a target substance is deposited on the substrate surface, comprising: A method for producing a photochemical thin film, comprising steps g, c, and e. a. A step in which the reaction chamber is evacuated to degas molecules adsorbed on the substrate surface. (g) A process of repeatedly introducing the gas intermittently at appropriate intervals; (c) A process of maintaining the substrate at a predetermined temperature in order to control the amount of adsorption of the gas. e. A process of irradiating the temperature-controlled substrate with radiation of a selected wavelength and/or wavelength band emitted from a light source such as a lamp, laser, and/or infrared radiation plate to deposit a target substance on the surface of the substrate. 8. A method for producing a photochemical thin film, characterized in that the degassing in step a described in claim 7 brings the degree of vacuum in the reaction chamber to a pressure of 10-5 Torr or less. 9. A photochemical thin film manufacturing method, characterized in that the degassing in step a as set forth in claim 7 is performed by heating the substrate to 100° C. or higher. 10. A photochemical thin film manufacturing method, characterized in that the radiation irradiation in item e of claim 7 is performed intermittently at predetermined intervals. 11. A method in which a gas is adsorbed onto a substrate surface in a reaction chamber, the adsorbed molecules and/or the substrate surface are activated by radiation and/or heat, and a target substance is deposited on the substrate surface, the method comprising: a. A method for producing a photochemical thin film, comprising steps g, c, e, and h. a. A step in which the reaction chamber is evacuated to degas molecules adsorbed on the substrate surface. (g) A process of repeatedly introducing the gas intermittently at appropriate intervals; (c) A process of maintaining the substrate at a predetermined temperature in order to control the amount of adsorption of the gas. e. A process of irradiating the temperature-controlled substrate with radiation of a selected wavelength and/or wavelength band emitted from a light source such as a lamp, laser, and/or infrared radiation plate to deposit a target substance on the surface of the substrate. h Exhaust the gas to below 10-3Torr,
A process of heating an optical window through which radiation passes by irradiating radiation and/or using a heat conduction method under the following pressure to degas the gas adsorbed on the side wall surface of the reaction chamber of the optical window.